On Tue 29-03-11 21:15:59, Zhu Yanhai wrote:

Michal,

Hi,

Maybe what we need here is some kind of trade-off?
Let's say a new configuable parameter reserve_limit, for the cgroups
which want to
have some guarantee in the memory resource, we have:

limit_in_bytes > soft_limit > reserve_limit

MEM[limit_in_bytes..soft_limit] are the bytes that I'm willing to contribute
to the others if they are short of memory.

MEM[soft_limit..reserve_limit] are the bytes that I can afford if the others
are still eager for memory after I gave them MEM[limit_in_bytes..soft_limit].

MEM[reserve_limit..0] are the bytes which is a must for me to guarantee QoS.
Nobody is allowed to steal them.

And reserve_limit is 0 by default for the cgroups who don't care about Qos.

Then the reclaim path also needs some changes, i.e, balance_pgdat():
1) call mem_cgroup_soft_limit_reclaim(), if nr_reclaimed is meet, goto finish.
2) shrink the global LRU list, and skip the pages which belong to the cgroup
who have set a reserve_limit. if nr_reclaimed is meet, goto finish.

Isn't this an overhead that would slow the whole thing down. Consider
that you would need to lookup page_cgroup for every page and touch
mem_cgroup to get the limit.
The point of the isolation is to not touch the global reclaim path at
all.

3) shrink the cgroups who have set a reserve_limit, and leave them with only
the reserve_limit bytes they need. if nr_reclaimed is meet, goto finish.
4) OOM

Does it make sense?

It sounds like a good thing - in that regard it is more generic than
a simple flag - but I am afraid that the implementation wouldn't be
that easy to preserve the performance and keep the balance between
groups. But maybe it can be done without too much cost.

Thanks
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>